The present invention relates to a method of connecting a flat cable to a connecting terminal, a connecting apparatus, and a connecting state determining method.
A conventional wire harness for use in a vehicle is typically comprise of wires each having a conductor of circular shape in cross-section covered with an insulating material. To establish electrical connections between wires of a wire harness or between wires and vehicle-mounted electrical equipment units, connecting terminals are attached to the conductors of the wires by means of crimping or insulation displacement.
To determine pass/fail of a crimping state or an insulation displacement state of the connecting terminal with the conductor, a method is known which takes advantage of a load pattern that changes with time during an operation of attaching a connecting terminal to a wire (Japanese Unexamined Patent Publications Nos. Sho 63-281071, Hei 10-125437). Based on such a determining method, a quality control system has also been established.
In recent years, with the trend of a complicated installation of wires and a reduction in size of connecting terminals, flat cables have been used in place of the conventional wire harnesses, and new connecting terminals called pierce terminals have been used corresponding to the flat cables.
The flat cable used in place of the wire harness is utilized in a module which is disposed in a narrow space or integrated with a vehicle component such as ceiling, door, and dash board. As shown in FIG. 17, a flat cable 1 has flat conductors 1a arranged in parallel and covered with an insulating material 1b. The conductors 1a are made, for example, of copper, aluminum or the like of 0.15 to 0.2 mm in thickness and approximately 1.5 to 2.5 mm in width Wc. The insulating material 1b is, for example, a polyethylene terephthalate (PET) film of 0.09 mm in thickness, or a less expensive polybuthylene terephthalate (PBT), or the like.
As shown in FIG. 18, a connecting terminal 3 has crimp pieces 3b arranged to opposite to one another on both sides of a substrate 3a and is provided at one end with a female terminal 3c. The substrate 3a is slightly narrower than the conductor 1a in width Wt which is set, for example, in a range of approximately 1.2 to 2.0 mm. FIG. 19 shows a connecting terminal 5 which has a female terminal 5c and crimp pieces 5b alternately arranged on a substrate 5a. 
To connect the connecting terminal 3 to the flat cable 1, the crimp pieces 3b are pierced into a desired conductor 1a at desired positions, and the leading ends of the penetrating crimp pieces 3b are bent inward in an arc shape to hold the desired conductor therebetween. In this way, the connecting terminal 3 is electrically connected to the desired conductor 1a of the flat cable 1.
The flat cable 1 having the connecting terminal 3 connected to the desired conductor 1a in the above manner poses a problem that an electrical connection between the conductor 1a and the crimp pieces 3b is not stable, thus entailing a variation. In addition, with regard to the connection with the flat cable 1 and the connecting terminal 3, no method has been established for determining pass/fail of the connection, although a determination method is established for the conventional connecting terminal. Thus, the provision of a method of determining a connecting state has been desired.
It is an object of the present invention to provide a method of connecting a flat cable to a connecting terminal, which achieves a stable electrical connection between a conductor of the flat cable and crimp pieces of the connecting terminal, a connecting apparatus, and a connecting state determining method.
To achieve the above object, according to one aspect of the present invention, there is provided a method of connecting a flat cable to a connecting terminal, in which the flat cable having a plurality of flat conductors, arranged in parallel and having surfaces thereof covered with an insulating material, is connected to the connecting terminal, by piercing a plurality of crimp pieces, formed integrally with a substrate of the connecting terminal, into a desired conductor of the flat cable and by inwardly bending leading ends of the crimp pieces penetrating the flat cable to hold the desired conductor therebetween. The method comprising the steps of piercing the crimp pieces into the desired conductor with a gap left between the substrate and the flat cable, and bending the leading ends of the crimp pieces while maintaining a contact position unchanged at which each of the crimp pieces penetrating the conductor is in contact with the conductor.
Preferably, the crimp pieces are urged simultaneously from the substrate and from the leading ends of the crimp pieces when the leading ends are bent.
Preferably, an urging force for urging the substrate is set to be larger than an urging force for urging the leading ends of the crimp pieces.
According to another aspect of the present invention, there is provided a method of connecting a flat cable to a connecting terminal, in which the flat cable, having a plurality of flat conductors arranged in parallel and having surfaces thereof covered with an insulating material, is connected to the connecting terminal, by piercing a plurality of crimp pieces, formed integrally with a substrate of the connecting terminal, into a desired conductor of the flat cable and by inwardly bending leading ends of the crimp pieces penetrating the flat cable to hold the desired conductor therebetween. The method comprises the step of forming cut ends in the desired conductor by means of the plurality of crimp pieces pierced into the desired conductor, each cut end extending along an inner face of a corresponding one crimp piece and in contact with the inner face with a constant contact pressure over substantially the entire length of the cut end.
According to a further aspect of this invention, there is provided a method of connecting a flat cable to a connecting terminal, in which the flat cable, having a plurality of flat conductors arranged in parallel and having surfaces thereof covered with an insulating material, is connected to the connecting terminal, by piercing a plurality of crimp pieces, formed integrally with a substrate of the connecting terminal, into a desired conductor of the flat cable and by inwardly bending leading ends of the crimp pieces penetrating the flat cable to hold the desired conductor therebetween. The method comprises the steps of forming cut ends in the desired conductor by means of the plurality of crimp pieces pierced into the desired conductor, each cut end extending along an inner face of a corresponding one crimp piece and in contact with the inner face with a constant pressure over substantially the entire length of the cut end, and inwardly bending the leading ends of the crimp-pieces penetrating the flat cable, while maintaining a contact state of the cut ends with the crimp pieces unchanged.
According to another aspect of the present invention, there is provided a connecting apparatus for connecting a flat cable to a connecting terminal, in which the connecting apparatus connects a flat cable having a plurality of flat conductors arranged in parallel and having surfaces covered with an insulating material to a connecting terminal by piercing a plurality of crimp pieces, formed integrally with a substrate of the connecting terminal, into a desired conductor of the flat cable, and by inwardly bending leading ends of the crimp pieces penetrating the flat cable to hold the desired conductor therebetween. The connecting apparatus comprises a receptacle on which the flat cable held at a predetermined position is placed, the receptacle having a pair of receiving grooves for receiving the crimp pieces, and a bending recess for bending the leading ends of the crimp pieces; an urging member having an urging tool, disposed opposite the receptacle with the flat cable interposed therebetween, for urging the substrate of the connecting terminal, and a guide member for guiding movements of the urging tool; first driving means having elevating means for moving the receptacle up and down, and a moving means for moving the receptacle to selectively place the receiving groove or the bending recess of the receptacle to opposite the connecting terminal; second driving means for urging the urging tool toward the substrate; and control means for controlling the operation of the connecting apparatus.
Preferably, the receptacle has a partition formed with the pair of receiving grooves, and the partition comprises a pressurizing incline plane at an entrance of each of the receiving grooves for forming cut ends in the desired conductor by means of the crimp pieces pierced into the desired conductor, each cut end extending along an inner face of a corresponding one crimp piece and in contact with the inner face with a constant contact pressure over substantially the entire length of the cut end.
Preferably, the urging member comprises a first sensor for detecting a load acting on the crimp pieces when the substrate is urged by the urging tool to pierce the crimp pieces into the flat cable, and a second sensor for detecting a displacement amount of the crimp pieces with a movement of the urging tool, wherein information detected by both the sensors is output to the control means.
Preferably, the control means receives load information from the first sensor and displacement amount information from the second sensor, and determines a connecting state of the crimp pieces to the conductor when the flat cable is connected to the connecting terminal.
Preferably, the receptacle comprises a top dead center position adjusting mechanism for adjusting a top dead center position of the receptacle.
Preferably, the urging member comprises a bottom dead center position adjusting mechanism for adjusting a bottom dead center position of the urging tool.
According to another aspect of this invention, there is provided a connecting state determining method for determining a connecting state of a connecting terminal to a flat cable having a plurality of flat conductors arranged in parallel and having surfaces thereof covered with an insulating material, in which the connecting state is determined when a desired conductor of the flat cable is connected to the connecting terminal by piercing a plurality of crimp pieces formed integrally with a substrate of the connecting terminal into the desired conductor and by inwardly bending leading ends of the crimp pieces penetrating the flat cable to hold the desired conductor therebetween. The connecting state determining method comprises the step of determining the connecting state of the crimp pieces to the desired conductor by comparing a piercing load determined when the crimp pieces are pierced into the flat cable and a normal piercing load determined in advance and observed when crimp pieces are normally pierced into a flat cable.
Preferably, the piercing load is determined based on a difference between a maximum load and a minimum load acting on the crimp pieces measured when the crimp pieces are pierced into the flat cable, the minimum load being measured after the maximum load is reached.
The foregoing and other objects, features and advantages of the present invention will become more apparent from the following detailed description based on the accompanying drawings.